1. Field of the Invention
The present invention relates to a phosphor used for a display device such as a CRT, a PDP, an FED and an EL, and a lighting apparatus and the like such as an LED, a vacuum fluorescent display and a fluorescent lamp, and a production method of the same, and a light source and an LED, and particularly relates to a phosphor excited by ultraviolet and blue light and the like, and emitting visible light or white light and the production method of the same, a method of shifting an emission wavelength of the phosphor, and a light source, an LED and the like using the phosphor.
2. Description of the Related Art
An electric discharge fluorescent lamp, an incandescent lamp and the like which are used as lighting devices at present have various problems such as inclusion of a harmful substance such as mercury and the short life span. However, the LEDs emitting blue light and ultraviolet light have been developed one after another in recent years, and the research and development have been increasingly conducted on the feasibility of combining ultraviolet to blue light generated from the LEDs with phosphors having excitation bands in the wavelength region of ultraviolet to blue color to thereby make a white light, and using the white light as the illumination of the next generation. This white light LED illumination generates less heat and is constructed by a semiconductor element and phosphors, and therefore it has the advantages of long life span without being burnt out as the conventional incandescent lamp and of disuse of a harmful substance such as mercury, and is an ideal lighting device.
Here, in order to obtain white light by combining the aforementioned LED with phosphor, two methods are generally considered. One is for obtaining white light emission by combining the LED emitting blue light with the phosphor, which is excited by receiving the blue light emission and emits yellow light, and combining the blue light emission with the yellow light emission.
The other one is a method for obtaining white light emission by RGB and other light by combining an LED emitting near-ultraviolet and ultraviolet light, and a phosphor emitting red (R) light, a phosphor emitting green (G) light, a phosphor emitting blue (B) light after the phosphor are excited by receiving the near ultraviolet and ultraviolet light emission, and the others. This method for obtaining white light emission by the RGB and other light makes it possible to obtain optional light emission color other than white light in accordance with the combination and mixture ratio of the RGB and other phosphors, and therefore has a wide application range as the lighting device. As the phosphors used for this purpose, for example, Y2O2S:EU, La2O2S:Eu, 3.5MgO.0.5MgF2.GeO2:Mn, (La, Mn, Sm)2O2S.Ga2O3:Eu are cited as red phosphors, for example, ZnS:Cu,Al, SrAl2O4:Eu, BAM:Eu,Mn are cited as green phosphors, for example, YAG:Ce is cited as a yellow phosphor, and for example, BAM:Eu, Sr5(PO4)3Cl:Eu, ZnS:Ag, (Sr, Ca, Ba, Mg)10(PO4)6Cl:Eu are cited as blue phosphors. By combining these RGB and other phosphors with a light emitting portion such as an LED which emits near ultraviolet and ultraviolet light, it is possible to obtain a light source and a lighting device including an LED which emits white or a desired color.
As for white LED illumination by the combination of the blue LED and the yellow phosphor (YAG:Ce), light emission of long wavelength side in the visible light region is insufficient. Therefore, light emission of white slightly tinged with blue is provided, and light emission of while slightly tinged with red as an electric bulb cannot be obtained.
As for white LED illumination by the combination of the near ultraviolet and ultraviolet LED and RGB and other phosphors, the red. phosphor out of the phosphors of three colors is low in the excitation efficiency in the long wavelength side as compared with the other phosphors, and low in the emission efficiency. Therefore, the mixture ratio of only the red phosphor has to be increased, which causes the shortage of the phosphors for enhancing the luminance, and thus white color with high luminance cannot be obtained. Further, the emission spectrum of the phosphor is sharp, and therefore there exists the problem of unfavorable color rendering properties.
Therefore, there are recently reported an oxynitride glass phosphor having good excitation in the long wavelength side, and capable of providing the light emission peak with wide half band width (for example, see Patent Document 1), the phosphor using sialon as the host material (for example, see Patent Documents 2 and 3), and the phosphor containing nitrogen of silicon nitride series or the like (for example, see Patent Documents 4 and 5). The phosphor containing nitrogen has a large ratio of covalent bond as compared with oxide series phosphors. Therefore, the phosphor has the characteristic of having a good excitation band in the light of wavelength of 400 nm or more, and receives attention as the phosphor for white LED.
The inventors of the present invention have also reported the phosphor containing nitrogen, which has a favorable excitation band for the light of the ultraviolet to visible (250 to 550 nm) wavelength region emitted from the light emitting element emitting light in blue and ultraviolet. (See Patent Document 6.)
[Patent Document 1] Japanese Patent Application Laid-open No. 2001-214162
[Patent Document 2] Japanese Patent Application Laid-open No. 2003-336059
[Patent Document 3] Japanese Patent Application Laid-open No. 2003-124527
[Patent Document 4] Translated National Publication of Patent Application No. 2003-515655
[Patent Document 5] Japanese Patent Application Laid-open No. 2003-277746
[Patent Document 6] Japanese Patent Application No. 2004-055536
In order to enhance light emission properties of visible light or white light, in the light source including the LED emitting visible light and white light by combination of the light emitting element emitting blue and ultraviolet light with the phosphor having the excitation band for the wavelength region of ultraviolet to blue emitted from the light emitting element, enhancement of the emission efficiency of the light emitting element and phosphor is naturally required, and at the same time, light emission color (color chromaticity, emission wavelength, luminance) of the phosphor is also important. In addition, it is considered that the demand for the phosphor of light emission color and excitation band are each optimized in accordance with the use purpose of the LED, light source and the like will increase in the future. Here, the inventors have conceived the problems as will be explained hereinafter.
First, the problem about the luminance concerting the light emission color of the phosphor will be explained.
Even when the intensity of the light emission generated by the phosphor is physically the same, blue light of the short wavelength and red light of the long wavelength are felt dark in the visual sense of a human being as compared with yellow light and green light. This is because the wavelength which is felt the brightest in the human visual sensitivity is in yellowish green light in the vicinity of 555 nm. Accordingly, in the emission wavelength emitted by the phosphor, the light of the same color tone can be felt brighter by a man by increasing the ratio of this wavelength. As a result, when the phosphor with high ratio of the yellowish green light in the emission light wavelength is used, the luminance is enhanced, and therefore it is the problem to develop such a phosphor.
Next, the problem about the color rendering properties concerning light emission color of a phosphor will be explained.
Considering the light emission color of a phosphor also from the viewpoint as illumination, the light emission color is demanded to be a broad emission spectrum without a gap from blue to red when combined with the light emitting portion of ultraviolet to blue. For example, a YAG:Ce yellow phosphor, which is a general phosphor, has the emission wavelength in the vicinity of about 560 nm, and can be said to be the phosphor having the emission spectrum of the best emission efficiency for the visual sensitivity. However, when white light is to be obtained by combining the YAG:Ce yellow phosphor with the blue LED, sufficient luminance is obtained in the viewpoint of the aforementioned luminance (visual sensitivity), but the light emission color in the long wavelength side, corresponding to red becomes insufficient. Therefore, the obtained emission light becomes white emission light slightly tinged with blue, and white emission light slightly tinged with red as the emission light of the incandescent lamp cannot be obtained. Therefore, when white light generated by combining the YAG:Ce yellow phosphor with the blue LED is emitted to a red object, the phenomenon in which red looks dark occurs, and which becomes a problem in the color rendering properties. As a method for solving the problem of the color rendering properties, it is required to realize the light emission of the spectrum from blue to red without a gap by further adding red light to yellow light emitted by the YAG:Ce yellow phosphor, and in order to obtain the red light, it is the problem to develop a phosphor of red color having the color rendering properties and luminance properties.
Further, the problem concerning the excitation range of the excitation light of the phosphor will be explained.
Seeing the aforesaid YAG:Ce yellow phosphor from the viewpoint of enhancement of the emission efficiency of the light emitting element for exciting a phosphor and the phosphor, the YAG:Ce yellow phosphor is in the excitation range with favorable efficiency when it is made to emit light with blue light emitted by the blue LED. However, when it is made to emit light with near ultraviolet and ultraviolet light emitted by the near ultraviolet and ultraviolet LED, the YAG:Ce yellow phosphor is out of the excitation range with favorable efficiency, and therefore sufficient light emission is not obtained. The cause of this is that the excitation range with favorable efficiency for the YAG:Ce yellow phosphor is narrow.
When the YAG:Ce yellow phosphor is made to emit light with blue light emitted by the aforementioned blue LED, the problem that the excitation range with favorable efficiency for the YAG:Ce yellow phosphor is narrow leads to the situation in which the wavelength balance of the blue and yellow is lost as a result that the emission light wavelength of the blue LED is out of the optimal excitation range of the YAG:Ce yellow phosphor due to the variation of the emission light wavelength caused by the variation in the light emitting element at the time of production of the blue LED. If such a situation is brought about, there arises the problem that the color tone of the white light, which is obtained by synthesizing blue light and yellow light, changes. Here, the variation in the emission wavelength following the production of the LED cannot be avoided, and therefore, in order to avoid the change in the color tone, it is the problem to develop the phosphor having the properties that the range of the excitation band is wide and flat.
The present invention is made in view of the aforementioned problems, and has its object to provide a phosphor, of which emission wavelength can be optionally set the region with high visual sensitivity of a human being, thereby making it possible to enhance the luminance in the region, emitting light of red color having color rendering properties and luminance properties, and has the excitation band for the light in the wide wavelength region of the ultraviolet to visible light (250 nm to 600 nm) emitted from the light emitting portion, when the phosphor is used in combination with the ultraviolet to visible light emitting portion, and a production method of the same, a method for shifting the emission wavelength of the phosphor, and a light source and a LED using the phosphor.